A 3-Minute Overview of Telephony, the Internet & VoIP

PSTN, PBX, lines & trunks: The Conventional Phone System

The conventional telephone system is generically referred to as the Public Switched Telephone Network (PSTN).

Dating to the late 1800's, this now huge network was built on the basic concept of a phone connection as being the electrical equivalent of two tin cans and a string.

Within the PSTN, subscriber lines radiate out to individual homes and businesses in a given service area from the local exchange, (also called a central office or CO). From the beginning, subscriber lines have been analog, and for the most part remain so today.

Within the exchanges, switches connect subscriber lines on demand to other subscriber lines, or to lines that run between exchanges, called trunks. Originally, switching was accomplished via human operators and manually-operated switchboards, then mechanical switches, and now digital switches.

Today, any sufficiently large business may have its own internal switchboard exchange, usually called a Public Branch Exchange or PBX. The PBX connects individual lines within the office to each other, or through a number of trunk lines to the rest of the PSTN and thus the world.

The Internet and IP

Like the PSTN, the Internet is a network. However, instead of carrying analog voice signals on temporarily-dedicated paths between telephones, the Internet carries packets of digital data along shared paths between computers.

For path sharing to work, each device must have a unique address on the network, each packet of information must carry a destination address, and to keep it all straight, everything must conform to a basic set of operating rules called Internet Protocol or IP.

Data over PSTN: So That's What a Modem Does

Most of us are familiar with the idea of transmitting digital data over the phone system or PSTN. We use a modem (modulator / demodulator) to translate data into modulated tones within the same range as the human voice so that they can be transmitted across the PSTN voice network. Another modem must be at the other end of the connection to receive the tones and demodulate them, extracting the original data.

This approach is used for fax transmission and computer-to-computer communications. We might call it Data over PSTN or DoPSTN—though we don't.

Voice over Internet Protocol

Voice over Internet Protocol (VoIP) is the parallel universe of DoPSTN. Instead of translating digital data and transmitting it over a voice network using modems, we translate analog voice signals and transmit them over a digital data network using codecs (coder/decoders).

As with modems, a compatible codec must be at the other end to establish a point-to-point connection.

Instead of a telephone number to identify an end-point, a VoIP terminal has an IP address just like a web site.

How VoIP Can Work for You

With the PSTN, telephone costs increase with distance. With the Internet, costs increase with bandwidth (the amount of data you need to move per unit time).

VoIP can save you money if...

• your business has two or more locations, each with an existing broadband Internet connection (T1, cable/DSL modem etc.), and
• significant voice traffic occurs between locations, with associated long-distance charges.

Using QTelnet FreeRide VoIP solutions, inter-office voice communications are accomplished through your existing Internet connections, thus eliminating the normal long distance charges.

In many cases, no additional bandwidth will be required, thus your Internet costs will not change. The incremental cost of adding a FreeRide VoIP system will be limited to the up-front cost of the equipment alone, and with no ongoing fees, cost recovery soon gives way to continuous savings.

If a high volume of voice communications is anticipated, additional bandwidth may be needed. However, straightforward economic analysis will show that a net ongoing savings will still be realized in most cases.

How FreeRide VoIP Components Integrate With Existing Equipment

QTelNet FreeRide VoIP components require an access point to a broadband Internet connection. Although site-dependent, this is typically effected via existing network equipment in much the same fashion as adding a computer.

FreeRide Gateways are extraordinarily flexible bridges between networks and conventional telephony equipment. The compact, unobtrusive units can sit at an individual workstation. However, if your office has a PBX, a single FreeRide Gateway can extend VoIP access to everyone via their existing desk sets.

Why Doesn't the PSTN use VoIP?

In fact, the public system has been making use of digital voice transmission for decades. The ability to transmit many calls on a single signal path, making far more efficient use of physical resources, is but one of the compelling advantages of digital voice methods. It saves the telephone companies a lot of money.

However, for subscribers, the same cost structure that was established back in “tin can” times remains to this day.